Heating, ventilating, and air conditioning control systems have been widely developed based on pneumatic as well as electronic control components. Pneumatic control systems may rely on the flow of air to transmit control and operating signals to the various control and operating components. Electronic and electrical control systems which include electrical control and operating signals to operate electrical devices have been widely used in various industrial and institutional control systems, including heating ventilating and air conditioning systems. With significant advances in electronic logic devices, and particularly small digital computing devices, various compound control systems have been developed employing pneumatic sensing and actuating devices with interposed electronic signal processing devices. Thus the advance of electronic logic devices such as the digital computers have resulted in a greater capability of manipulation and processing of various signals, with the ability to process complex control algorithms based upon sensed conditions, with and without modifications. Modern electronic devices also permit improved communication with other electronic instrumentation and controlled devices. In order to adapt the improved logic-type digital devices to the pneumatic controls, the electrical signals must be converted to an appropriate form for controlling transmission of pneumatic pressure signals to pneumatic control devices such as pneumatic actuators and the like.